I'm using version 2013 and Edit -> Transpose -> "Transpose # of semitones" does not work with 12 or -12 semitones set. I have to use Ctrl-Alt-5, or Transpose DOWN 1 semitone, 12 times.
The terminology you use in your description sounds like you may be trying to use an Audio Effect on a MIDI track.
Back around 2013 the path to transpose MIDI would be :
'Edit-Pitch Transpose MIDI music'
Then the option would be 'Value' instead of 'semitones'.
I think Semitones was used in the Audio Edit plugin (not the MIDI) around that version.
Maybe you need to make sure you are selecting the correct Edit option initially. Just a thought.
LynB's solution may work also, as it circumvents the selection in the first place.